1. Field of the Invention
The present invention relates to laser recording film of the type having an opaque coating deposited on one side. A selectively directed laser beam generates transparent areas on the film for projection onto a viewing screen.
2. Description of the Prior Art
Laser recording films are employed in a species of visual presentation equipment adapted to display large amounts of data on a real time basis. The visual presentation equipment includes a computer controlled laser beam which illuminates selected surface portions of the film to change the light transmissibility of the illuminated surface portion from opaque to substantially transparent. Large amounts of data, including alpha numeric characters and graphical depictations, can be rapidly "written" onto the film. Projection means, including a tungsten filament light source and projection optics, form an image from the "written" information for projection onto a viewing screen. A more detailed explanation of the visual presentation equipment may be had by refering to U.S. Pat. No. 3,961,334, the disclosure of which is incorporated herein.
Heretofor laser recording films have been fabricated from a transparent film substrate having an opaque metallic coating applied to one side thereof. The film substrate may be a standard 35 mm format polyester film. A variety of metals, including bismuth and copper, have proven satisfactory. A transparent plastic or lacquer coating may be applied to the metallic coating to provide protection against abrasion.
Metal coated laser recording films can be fabricated using conventional thin film deposition techniques. The clean transparent film substrate is placed in an evacuation chamber and exposed to a source of metal vapors. The thickness of the metallic coating is accurately controlled by controlling the deposition duration and the metal evaporation rate. Coating thicknesses in the range of 0.05 microns to 0.10 microns are preferred. As is well known, conventional thin film deposition is a batch process requiring extreme cleanliness and expensive vacuum deposition equipment. A high degree of skill is necessary to produce consistently uniform coatings.
When a surface portion of the laser recording film is irradiated by a laser beam having a circular cross section, the temperature of the metal within the irradiated area quickly rises to the metal's melting point. Surface tension then causes the molten metal to migrate in a radially outward direction to the periphery of the irradiated area to form an aperture or "window". The molten metal concentrates at the periphery in a random manner and forms an irregular peripheral rim. Trailings or globules of metal which do not migrate to the rim zone adhere in a random manner to the transparent film substrate within the aperture and diminish light transmissibility thru the aperture. The molten metal may also roughen the film surface within the aperture and alter the light transmissibility of the film substrate.
While the performance of metalized laser recording films have been generally satisfactory, the peripheral rim surrounding the aperture, the presence of globules within the aperture, and the roughened film substrate surface within the aperture limit the sharpness and visual qualities of the projected image. Also thin film vapor deposition techniques are a batch rather then a continuous process and require a large capital investment in vacuum production equipment.
Applicant's invention provides a laser recording film with an opaque, plastic/dye coating having improved aperture formation characteristics to provide improved projection image sharpness and visual quality. The applicant's laser recording film can be economically produced on a continuous process basis compatible with standard wet coating film manufacturing machinery.